1. Field of the Invention
The present invention relates to a method for producing structured electrodes and especially organic electra-luminescent components with structured electrodes. The components are used in displays and the like and further comprise structured metal electrodes, The electrode is supported by multiple layers of varying widths and heights such that in combination with other supports, active organic layers may be tightly packed into a display area. A possible arrangement includes an electrode placed atop the active layers.
2. Description of Related Art
Thin layers, in particular those with a thickness of 1 nm to 10 μm, find diverse technological applications, for example: semiconductor production; and microelectronic, sensory and display technologies. Production of the organic electro-luminescent components usually includes structuring necessary layers; whereas the necessary structure sizes range from the sub-μ-area to the entire substrate area. In addition, the required component form varieties are practically unlimited.
In general, there are many available lithographic processes available for structuring electrodes. What most of these processes have in common is that the layers to be structured come into contact with more or less caustic chemicals, including photoresists, solvents, developing fluids, and corrosive gases. Such contact can lead to corrosion or at least damage of the layers to be structured. This is often the case with organic light emitting diodes.
Organic Light Emitting Diodes (OLEDs), i.e. electro-luminescent diodes, are predominately used in displays. Examples of such applications are set out in U.S. Pat. Nos. 4,356,429 and 5,247,190. A method of producing electrodes in general is disclosed in German patent registration reference 197 45 610.3. The structure and production of OLED displays typically occurs as follows.
A substrate, for example glass, is coated entirely with a transparent electrode—bottom electrode, anode. The bottom electrode can comprise indium-tin-oxide (ITO). To produce pixel-matrix-displays, the transparent bottom electrode as well as the later formed top electrode (cathode), is structured. Accordingly, both electrodes are usually structured in the form of parallel strip conductors. The strip conductors of the bottom and top electrodes tend to run vertically with respect to each others. The structuring of the bottom electrode occurs via a photolithographic process which includes wet chemical etching methods, the details of which are known to one skilled in the art. The etched final structure obtainable with this method is essentially limited by the photolithographic steps and the consistency of the bottom electrode. According to the current state of the art, pixel sizes as well as non-emitting spaces between the pixels can be as small as a few micrometers. The lengths of the strip shaped strip conductors of the bottom electrode can be as large as many centimeters. According to current lithographic masking, emitting areas as large as several square centimeters can also be produced. The sequence of each emitting area can be regular (pixel-matrix-display) or variable (symbol presentations).
One or more organic layers are applied on a substrate, the substrate including the structured transparent bottom electrode. These organic layers may comprise polymers, oligomers, and low molecular combinations or mixtures thereof. To apply polymers, for example polyainilene, poly (p-phenylenevinylene) and poly (2-methoxy-5-(2′ethyl) hexyloxy-p-phenylenevinylene), generally liquid phase processes are used (application of a solution by spin coating or blading); while a gas phase deposition is preferred for low molecular and oligomer combinations (Evaporation or Physical Vapor Deposition, PVD). Examples of low molecular layers, such as positive charge transporting carriers include the following: N,N′-bis-(3-methylphenyl)-N,N′-bis-(phenyl)benzidine(m-TPD), 4,4′,4″-Tris-(N-3-methylphenyl-N-phenylamino)-triphenylamine (m-MTDATA) and 4,4′,4″-Tris-(carbazol-9-yl)-triphenylamine (TCTA). Hydroxychinoline-aluminium-III-salt (Alq) is used, for example as an emitter, which can be doped with suitable chromophores (quinacridone-derivates, aromatic hydrocarbons, etc.). If necessary, exemplary existing additional layers which influence the electro-optical characteristics as well as the long-term characteristics may be copper-phthalocyanine. The entire thickness of the layer sequence can range between 10 nm and 10 μm, typically in the range of 50 to 200 nm.
The top electrode usually comprises a metal which is generally applied by gas phase deposition (thermic deposition, sputtering or cathode rays deposition). Preferred compositions are base (therefore reactive metals, especially to water and oxygen), and include lithium, magnesium, aluminum and calcium as well as alloys of these metals. For the production of a pixel-matrix-order structure having metal electrodes, the structure is obtained generally by applying the metal through a mask opening.
A produced OLED-display, according to this method, may additionally contain electro-optical features such as: UV-filters, polarization filters, anti-reflection coatings, and (micro-cavities) known installations such as color conversion and color correctional filters. In addition, a hermetically-sealed packaging may be provided by which the organic electro-luminescent displays are protected from external environmental influences such as humidity and mechanical strains. Thin film transistors for individual picture elements (pixel) can be added.
For high resolution displays on which large informational content can be presented, a fine structuring of the metal electrodes in the form of strip conductors is necessary. For example the width of the strip conductors as well as the spacing in between must be structured in keeping with narrow tolerances in the microns. Herein, the width of a strip conductor can lie between 10 μm and several hundred micrometers, preferably between 100 and 300 μm. To reach a high filling factor (share of the active light emitting area versus the entire display area) it is also necessary that the spaces between the metallic strip conductors as well as the spaces between the strip conductors of the transparent bottom electrode be only a few micrometers. Established structuring techniques can not be used here because the existing active organic layers, i.e. the electro-luminescent materials, are not resistant to the necessary chemicals for such fine structuring.
By so called shadow masking, i.e. thin metals or segments with correspondingly formed openings for a desired structure, only layers can be structured and produced according to CVD or PVD (chemical vapor deposition, physical vapor deposition) methods. Furthermore, the obtainable resolution produces (based on the finite distance between masking and substrate) relatively inferior results and large areas (as a result of a bending of the shadow masking), cannot be realized in view of production engineering.
A lift off method for the production of structured metallizations by use of two separate photoresist layers is taught by German reference DE-A44 01 590 which produces relatively thick metal structures on semiconductor components.
Furthermore European reference EP-A-0 732 868 describes a method for the production of an organic electro-luminescent display device. For this, on a multiple number of first display electrodes, electrically insulated overhanging structures are produced, which are built up from a first layer, for example of polyamide, and a second layer of for example SiO2. Afterwards, organic functional layers for different color components or an only color component are applied in the areas between the electrically insulated structures by use of (shadows) masks, then the material for the second display electrode is precipitated on the organic functional layers and the electrically insulated structures.